Booster Engines - of all the (relatively) few types considered by Wiener,
the use of a booster engine was the only one of real practical
significance. One of the major failings of a steam locomotive is its
inability to deliver its full power output when starting up or
accelerating from slow speeds - any attempt to do so will result in a
slip. A booster engine mounted in either a forward or a trailing truck or
even the tender can be 'switched in' temporarily to apply extra power -
see http://en.wikipedia.org/wiki/Booster_engine.
The downside was that their use introduced an additional complication in
both maintenance and operation and they were only of intermittent use. The
idea never really caught on although some railways in the USA and
Australasia made attempts to make the concept work. This is a Franklin
Booster, taken from this page http://en.wikipedia.org/wiki/File:Franklin-Booster.jpg
which indicates that it is in the public domain (at least in the USA) as
it appeared in the the 1922 'Locomotive Cyclopedia of American Practice'.

The true Engerths (http://en.wikipedia.org/wiki/Engerth_locomotive)
were a variety of unsuccessful designs involving (internal) gearing
transmitting the drive and the transfer of some of the weight between tender
and locomotive - see elsewhere
in this section under geared locomotives although quite where in these
page the locomotive illustrated belongs is another matter! A modified version of the
former feature was developed by Orenstein and Koppel in the
Luttermöller locomotive. Stütz developed the latter feature, but it was
not widely adopted. Stütz tenders (Wiener's book uses 'Stutz') are seen on
some of the locomotives at Sudhono sugar mill in East Java, Indonesia. It is
therefore a moot point as to whether these are best described as 0-6-0
tender locomotives or 0-6-4 tank locomotives although they more closely
resemble the former from a distance:

The
Austrian narrow gauge 399 class are often called 'Engerths' but used the
same system (as confirmed by the designation 'D2st' in my copy of the
Krauss builders list where st = Stütztenderlokomotive) . They were
originally supplied to what is now known as the Mariazellerbahn and which
later worked for many years on the lines out of Gmund, This picture comes
from http://en.wikipedia.org/wiki/File:Austria_narrow_gauge_mh6.jpg
and may not be reproduced except under the conditions stated on that page;
It shows one of the locomotives returned to its first home - since
electrified, the current location of each of the six locomotives is given
in the first link at the top of this section.

2. Steam Tenders

Wiener divides steam tenders into those used permanently
and temporarily. They were never very fashionable, apart from the
technical problems arising from using articulation, fitting them to
locomotives with standard boilers led to them being short of steam.

In
the UK, River Esk was designed by Henry Greenly as a 2-8-2 tender engine, and built by Davey, Paxman Ltd. in
1923 for the Ranvenglass and Eskdale 15" gauge railway in what is now
Cumbria. The original valve gear was fitted in Colchester by the builders, with their Lentz poppet vales, however, these gave problems, but these were sorted by the addition of Walschaerts valve gear in 1928, by the Yorkshire Engine Co. They also fitted a 0-8-0 steam chassis under the tender, with their Poultney system, and this was supposed to supply extra power on the granite trains, but was unneeded and removed in 1931.
This picture originally appeared on this forum - http://s9.zetaboards.com/MRW_Forums/topic/7099776/1/,
apparently it is a scan of an old Ravenglass and Eskdale postcard:

A picture of 'River Mite' with another steam tender on the
same railway (as 4-6-0 + 0-6-4) appears at the end of the Binns
Bradford Barton book which has technical details.

Those in the 'temporary' class by and large worked in the
same way as 'booster engines' - see above - a feature that was (almost)
entirely restricted the the USA according to Wiener.